1. Field of the Invention
The present invention relates to a transflective thin film transistor substrate of a liquid crystal display device, and more particularly, to a transflective thin film transistor substrate and method of fabricating the same that is adaptive for simplifying its process.
2. Discussion of the Related Art
A liquid crystal display device controls the light transmissivity of liquid crystal, which has dielectric anisotropy, using electric field, thereby displaying a picture. For this, the liquid crystal display device includes a liquid crystal display panel to display a picture through a liquid crystal cell matrix, and a drive circuit to drive the liquid crystal display panel.
Referring to FIG. 1, a related art liquid crystal display panel includes a color filter substrate 10 and a thin film transistor substrate 20 which are bonded together with each other having a liquid crystal material 24 therebetween.
The color filter substrate 10 includes a black matrix 4, a color filter 6 and a common electrode 8 which are sequentially formed on an upper glass substrate 2. The black matrix 4 is formed on the upper glass substrate 2 in a matrix shape. The black matrix 4 divides the area of the upper glass substrate 2 into a plurality of cell areas in which a color filter is to be formed, and prevents the optical interference and external light reflection between the adjacent cells. The color filter 6 is divided into red R, green G, blue B in the cell area by the black matrix 4 to transmit red, green and blue lights respectively. The common electrode 8 supplies a common voltage Vcom to a transparent conductive layer, which is spread over the entire surface of the color filter 6, wherein the common voltage Vcom becomes a reference when driving the liquid crystal 24. And, to flatten the color filter 6, an overcoat layer (not illustrated) is additionally formed between the color filter 6 and the common electrode 8.
The thin film transistor substrate 20 includes a thin film transistor 18 and a pixel electrode 22, wherein the thin film transistor 18 is formed every cell area which is defined by the cross of a gate line 14 and a data line 16 in a lower glass substrate 12. The thin film transistor 18 supplies a data signal from the data line 16 to the pixel electrode 22 in response to a gate signal from the gate line 14. The pixel electrode 22 formed of a transparent conductive layer supplies the data signal from the thin film transistor 18 to drive the liquid crystal 24.
The liquid crystal material 24 having dielectric anisotropy rotates along the electric field formed by the common voltage Vcom of the common electrode 8 and the data signal of the pixel electrode 22 to control the light transmissivity, thereby making the gray level realized. The liquid crystal display panel further includes a spacer (not illustrated) to maintain the cell gap between the color filter substrate 10 and the thin film transistor substrate 20.
The color filter substrate 10 and the thin film transistor substrate 20 of the liquid crystal display panel are formed using a plurality of mask processes. One mask process includes a plurality of processes such as a thin film deposition (coating) process, a cleaning process, a photolithography process (hereinafter, referred to as a photo process), an etching process, a photo-resist peeling process, an inspection process and so on. In particular, the thin film transistor substrate includes the semiconductor process and requires a plurality of mask processes, thus its manufacturing process is complicated so that it becomes a material cause for the increase of the liquid crystal display panel manufacturing cost.
A liquid crystal display devices is generally classified into a transmissive type having a picture displayed using the light being incident from a backlight unit, a reflective type having a picture displayed by reflecting an external light such as a natural light, and a transflective type using an advantage of both the transmissive type and the reflective type.
There is a problem that the power consumption of a backlight unit is high in the transmissive type while the reflective type depends on the external light so as not to be able to display the picture in a dark environment. On the other, the transflective liquid crystal display device operates in the reflective mode if the external light is sufficient and in the transmissive mode if the external light is not sufficient, thus it can reduce the power consumption more than the transmissive liquid crystal display device and it is not restricted by the availability external light, which is different from the reflective liquid crystal display device.
To this end, the transflective liquid crystal display panel includes each pixel divided into a reflection area and a transmission area. Accordingly, a reflection electrode, formed in the reflection area, and an insulating film for making light paths in both the reflection area and the transmission area the same should be further added in a transflective thin film transistor, as compared to the thin film transistor as illustrated in FIG. 1. As a result, because the number of mask processes must be increased, there is a problem that the manufacturing process of the related art transflective thin film transistor substrate is complex.